I echo two things here.
The 600 spine if shooting a 125 grain broadhead/field point. 500 spine if you are wanting to shoot heavier. My draw length is 26" and I shoot 43-49# at my draw length with 600 and 500 spine arrows. I simply shoot heavier broadheads/field points with the 500 spine.
I cut my arrows 1-1.5 inches longer than my draw length. I don't like the arrow out more than 1.5" from the back of the shelf.
If you want I'll send you a couple fletched up Axis Trads in 500 spine you can have and test. I'll also include a couple 600 spine Axis. Both will have feathers. No charge, I'll cover shipping too. Just PM me a shipping address if you want em.
I paper tune from 6-8 feet to tune and proof. When I achieve a "bullet hole" I put a broadhead on and shoot for a group.
All of this said, you need to get your form solid so you'll be tuning the arrow rather than yourself. I shoot recurves and compounds, sometimes like today both in the same session. Other than one has a release aid and sights and the other doesn't, no difference is shooting form.